This proposal describes a five year mentored research project with the goal of characterizing the innate and acquired immune responses to two novel pneumococcal T cell antigens. The principal investigator's clinical background as a pediatric infectious diseases specialist and scientific background in pneumococcal T cell antigen discovery serve as the foundation on which these research endeavors will build. Successful completion of this project will provide the principal investigator with the experience in molecular microbiology, expression analysis and innate immunology methodologies necessary for transition to independence as an investigator in bacterial pathogenesis and evaluation of host pathogen interactions. This work will occur within the research laboratories of the Division of Infectious Diseases at Children's Hospital Boston with abundant scientific resources available within the division and the surrounding community of Harvard Medical School. For scientific and career guidance, this work will progress with the mentorship of Dr. Richard Malley, an expert in the field of pneumococcal immunity and vaccine development, and the co-mentorship of Dr. Douglas Golenbock, an expert in innate immune mechanisms. There has recently been a paradigm shift in the understanding of mechanisms of acquired immunity to numerous mucosal pathogens. Work of the Malley lab and others has shown that IL-17A-secreting CD4+ T cells (TH17 cells) mediate resistance to colonization with Streptococcus pneumoniae in an antibody- independent manner. From proteomic screens completed with Dr. Malley and collaborators, the principal investigator has identified several novel antigens based on their recognition by TH17 cells of mice immunologically protected from pneumococcal colonization. Several of these proteins protect animals from pneumococcal colonization when used as mucosal vaccines. Of these proteins, two are lipoproteins that appear to activate the innate immune Toll-like receptor (TLR) 2. Based on the hypothesis that the innate immune stimulatory potential of these proteins is contributing to the protection they confer, the proposed work will further characterize these proteins with a focus on the interaction between the innate and acquired immune responses they elicit. This work proposes to determine 1) whether these proteins are TLR2 agonists, 2) the role of these proteins in pneumococcal pathogenesis and 3) the role of TLR2 in the generation of protective immune responses to these proteins. This study aims to elucidate the mechanism of immunity elicited by two proteins that may be strong candidates for a protein subunit pneumococcal vaccine and may enhance the understanding of pneumococcal interaction with the host immune system. Infections with Streptococcus pneumoniae account for an estimated 11% of mortality in young children worldwide making an affordable, serotype-independent pneumococcal vaccine a global health priority. A vaccine that prevents colonization would have a double-edged advantage, as it would reduce the major manifestations of pneumococcal disease and contribute to a reduction in transmission rates thereby enhancing the herd immunity conferred by immunization. Further characterization of candidate proteins and elucidation of the mechanism of immunity they elicit are critical to advance the development of a protein subunit vaccine that prevents colonization.